1. Field of the Invention
The invention concerns apparatus and methods for driving a vehicle utilizing a plurality of motors, and in particular to such apparatus and methods wherein an electrical motor is assigned to a switchable transmission and to a wheel of an axle of a vehicle.
2. Description of Related Technology
Electrical motors find increasing application today for driving vehicles, especially for driving utility vehicles in street traffic (see, for example, Wust, B., Muiller, R., and Lange, A., "An Electrical Single-Wheel Drive for the City Buses of the Future," DER NAHVERKEHR, 6/1994, Alba Fachverlag, Duisseldorf).
Electric motors have operating regions with very good efficiency and other operating regions with lower efficiency. When electrical motors, such as those described in the above article, are used in vehicles, the drive system is generally designed so that the majority of the operation takes place in the motor operating regions exhibiting an optimum efficiency. However, due to necessary rpm regions, operation in regions of lower efficiency cannot be avoided. Therefore, in various individual applications, a transmission is attached to the electric motor.
A disadvantage of some transmissions is the occurrence of an interruption of the traction force during switching (i.e. shifting gears), for example, when a claw gear is utilized. In some applications, in order to avoid such an interruption of the traction force, a more expensive transmission may be used, for example, a planetary gear with lamellar coupling or lamellar brake.
Due to an interruption of the traction force during the gear shifting or switching process, drive systems for street vehicles have utilized wheel gears with constant transmission (see, e.g., Wust, B., Muller, R., and Lange, A., "An Electrical Single-Wheel Drive for the City Buses of the Future," DER NAHVERKEHR, 6/1994, Alba Fachverlag, Dusseldorf).
Furthermore, automatic or automatically shiftable transmissions of the state of the art have not been used with electronic drives because of overly high energy use.